It was the photo seen around the world: Pope Francis, on his landmark visit to the US, bending down to kiss the head of a little girl on Market Street in Philadelphia.

That child was Gianna Masciantonio, a one-year-old girl who at the time was fighting for her life against a debilitating brain tumor.

Four weeks after she was born, doctors told Gianna's parents to start planning her funeral. Now, three years later, her tumor has completely disappeared.

It's a story made all the more incredible by that fateful day in September 2015, the day Gianna earned the nickname 'Miracle on Market'.

Gianna Masciantonio was dubbed the 'Miracle on Market' when she was kissed on the head by Pope Francis during his US visit in 2015. Months later, her inoperable brain tumor disappeared

When Gianna was born, by all appearances she looked to be a healthy baby girl.

But doctors realized something was wrong when she failed a hearing test at the four-week mark.

They then discovered the newborn had a massive tumor on her brain stem. It was inoperable. They were shocked Gianna had even survived the pregnancy.

Doctors told Kristen and Joey Masciantonio to put their baby girl in hospice care and prepare for her death, giving her weeks to live.

But the loving parents didn't give up hope.

They began contacting the best children's hospitals across the country, searching for advice and second opinions.

Now three years old, Gianna is continuing to defy doctors' predictions and thriving. Her family recently donated $50,000 to her hospital from their foundation

Gianna (pictured with one of her doctors) was given just weeks to live when doctors discovered she had a massive tumor on her brain stem

Meanwhile, the Catholic couple found solace in prayer. They began weekly Tuesday telephone meetings with family and friends to say the rosary.

It was one of the few things that offered them hope as they woke up every morning, unsure if they would find their baby alive or dead in her bassinet.

When news spread that the pope was coming to town, Kristen knew they had to be there.

The couple debated whether it'd be safe to take Gianna into the crowd but, after getting the green light from her doctor and a little help from a friend's FBI connection, the trip seemed destined to happen.

They were given a spot as close as possible to the street procession, and raised Gianna high above the crowd as the Popemobile came towards them.

Doctors told her parents to put Gianna in hospice care and begin planning her funeral. But they didn't give up hope

Two months after Gianna was kissed by the pope, she was correctly diagnosed with a rare blood disorder and it was discovered her tumor wasn't malignant after all